Clinical and Health Affairs

Hospital-Treated Dog Bites in Minnesota, 1998-2005

AbstractThis paper is the first to describe the incidence of hospital-treated dog bites in Minnesota using hospital discharge data supplemented with medical record review. The rate of hospital-treated dog bites rose 40% during the 8-year period studied, with the largest growth being seen in the number of emergency department (ED) visits. The highest rates of both hospitalization and ED treatment occurred among children ages 1 to 4 years. In most instances (75%), the victim was familiar with the dog(s) involved. The dog bites most often occurred in the home (48%) and yard (18%). Our findings emphasize the importance of physicians, especially pediatricians and family physicians, counseling parents about the importance of supervising their children when they are around dogs and teaching them safe behaviors around animals. Finally, this study validates the value of hospital discharge data for surveillance of hospital-treated dog bites.

Although a number of studies have demonstrated the health benefits of dog ownership, having a companion dog does not come without risk. Several recent high-profile dog-bite incidents in the Twin Cities have drawn attention to the very real potential of serious injury from a dog bite. According to the Centers for Disease Control and Prevention (CDC), approximately 368,000 individuals were treated in emergency departments (EDs) in 2001 for dog bites.1 The most recent national data on dog-bite–related hospital admissions from 1994 estimate 6,000 such incidents per year.2 A query of the CDC WONDER online injury mortality data set found that dog bites were an underlying cause of death for 24 individuals in the United States between 1999 and 2002.3 This paper is the first to describe the epidemiology of dog bites in Minnesota.

Methods Statewide discharge data from the Minnesota Hospital Association from January 1, 1998, to December 31, 2005, were analyzed. This data set included dog-bite cases that were treated in the hospital (the patient was hospitalized or treated in the emergency department [ED]). Cases were classified as dog-bite injuries if they had an external cause-of-injury code (E code) of E906.0 (dog bite). Death certificates from this same time period were manually reviewed to identify possible dog-bite–related fatalities. To collect data and information about the victims and dogs involved, a stratified sample of records of patients treated in 2001 and 2002 were selected for medical record review.

FindingsA total of 849 hospitalized patients and 24,584 treated in the ED between 1998 and 2005 had an E code of E906.0 (dog bite). One dog-bite–related death was identified during the study period. Dog-bite–related hospital charges totaled more than $18.6 million during the 8-year period. The median charges for ED treatment of dog bites increased 69% from $246 to $416, while the median charges for hospital treatment increased 42%, from $5,294 to $7,538 between 1998 and 2005. Rates of hospital-treated dog bites rose 40% during the study period (Figure 1); the majority of those were treated in the ED. The greatest incidence of dog-bite injuries—6.9 to 7.7 per 100,000 population—occurred between May and August. The incidence dropped to 3.4 to 4.3 cases per 100,000 population between November and March.

Children 1 to 4 years of age had the highest incidence of hospital-treated dog bites. However, the median age for patients hospitalized because of dog bites was 31 years and 18 years for those whose injuries were treated in the ED. Rates of hospital-treated dog bite injuries were inversely proportional to the median income of the communities in which the individuals resided.

A total of 752 records were selected for abstraction; 150 (20%) were excluded from analysis. Of those, 71 case records could not be located; 74 had already received hospital treatment; 4 were non-bite injuries (3 scratch injuries from dogs and 1 tick bite); and 1 case involved a nonresident. Activity/circumstances surrounding the dog bite are presented in Figure 2.

DiscussionThis study was subject to some limitations. First, in Minnesota, E coding is voluntary; therefore, it is possible that we missed dog- bite cases because they were not coded. Approximately 95% of both hospitalized and ED-treated individuals with a primary injury diagnosis code had a corresponding E code, and the percentage of injuries E coded increased over the 8-year period.

We found little information about the dogs in the medical record (dog breed was unknown or not documented in nearly 60% of cases, and previous bite history was unknown for 73% of dogs). There are conflicting arguments regarding the role of breed and a dog’s tendency to bite. The American Veterinary Medical Association Task Force on Canine Aggression and Human-Canine Interactions cautions that “singling out 1 or 2 breeds for control can result in a false sense of accomplishment” and “ignores the true scope of the problem and will not result in a responsible approach to protecting a community’s citizens.”4 According to Wright, there are at least 5 interacting factors that play a role in a dog’s tendency to bite: heredity, early experience, later socialization and training, health (medical and behavioral), and victim behavior.5

Seventy-four (11%) individuals were excluded from analysis because they had previously received hospital or ED treatment for their dog bite and were considered nonincident cases. Forty-three percent of those previously treated had a primary diagnosis of cellulitis or abscess when they returned for follow-up treatment, suggesting a fairly high complication rate. This finding, along with that of a previous study estimating that 20% to 25% of dog bites become infected, underscores the need for clinician education to ensure appropriate treatment at initial presentation.6

Our findings on seasonal variation of dog-bite rates mirror those of the CDC: There is an increase during warm-weather months (May through August) and a corresponding decrease during colder months (November through March).1

Higher rates of hospital-treated dog-bite injury were observed among residents of communities with lower median incomes. This may reflect a treatment bias because the poorer members of the community may not have access to treatment in a clinic or urgent care facility and instead may rely on the ED. It may also be related to factors such as population density, dog breed and origin (eg, shelter, pet store, or breeder), the number and age of children in a home where a dog is present, and whether dogs receive adequate nutrition, training, and exercise.

Our findings draw attention to several important public health issues. First, contrary to popular perception, stray dogs are rarely responsible for hospital-treated dog bites. The majority (75%) of victims were bitten by dogs that were known to them, which is consistent with previous findings.7-11 Second, a victim’s age is inversely related to risk.1,6,9,12,13 In Minnesota, the incidence of ED-treated dog bites was highest for children ages 1 year to 4 years (Table). This differs from previous national estimates from the CDC, which found the highest rates of ED-treated dog bites among children ages 5 to 9 years.1 Dog bites resulting in an open wound to the head were the most common injury (29%). The majority of these injuries occurred among children ages 1 year to 9 years, which is consistent with previous studies.1,8,9,13-15 On a positive note, Minnesota’s overall rate of ED-treated dog bites is lower than the national rate (62.4 per 100,000 population versus 129.3 per 100,000 population).1

When the activity or circumstance surrounding the bite was evaluated, some findings emerged that bear further investigation. First, the majority (96%) of bites to children younger than 1 year of age occurred when the child was provoking, teasing, or approaching the dog. This finding reinforces the need for continuous supervision of infants when they are around dogs. Second, among children ages 1 to 4 years and persons 80 years and older, the activity or circumstances surrounding the bite were unknown or not documented in 31% of cases. The individuals in these age groups are our most vulnerable citizens, which is of concern from a public health standpoint; we need to formulate intervention activities on their behalf. Finally, among children ages 5 to 14 years, walking, running, or biking past a dog was the leading cause of injury (31%). Because these situations are difficult to avoid, it is important to emphasize the importance of safe behaviors around dogs to children in this age group.

Bites from marauding packs of feral dogs are not a problem in Minnesota; very few of the cases analyzed (<3%) involved multiple dogs. Five percent occurred during law enforcement, and most of those happened in the 7-county Twin Cities metropolitan area. During the 2-year period covered by abstraction (2001 and 2002), an estimated 19 law enforcement-related dog-bite cases resulted in hospitalization, and 201 were treated in the ED. To reduce the number of law enforcement-related dog-bite injuries in Los Angeles, changing from doing “bite and hold” apprehension to a “find and bark” strategy resulted in a nearly 10-fold reduction in reported injuries and a decrease in the severity of those injuries.16

From a public health surveillance standpoint, our findings validated the high positive predictive value for the E906.0 (dog bite) code. This study confirms the utility of statewide hospital discharge data for surveillance of hospital-treated dog bites.

RecommendationsSo, what can be done to prevent dog bites? According to the literature, health care providers should provide patients with information about safe behaviors around dogs.1,4,17-20 Infants, children, and other vulnerable individuals should be supervised when they are around dogs.1 Dog owners need to socialize their dogs so that they learn how to behave appropriately around other dogs and people.1,4 Health care professionals also should support communitywide dissemination of information on proper care and treatment of dogs, enhancements to legislation on dangerous dogs (under Minnesota Statute section 347.50, a dog may be declared potentially dangerous if, when unprovoked, it bites a human or domestic animal, chases a person in an apparent attack mode, or has a “known propensity, tendency, or disposition to attack unprovoked, causing injury”), and education for veterinarians and human health care providers about normal and abnormal animal behavior so that they, in turn, can counsel their clients and patients.4 In the event that clinicians need information about human exposure to rabies, prophylaxis, and bite management, they can contact the Minnesota Department of Health’s 24-hour phone line at 651/201-5414 or 877/676-5414. MM

Heather Day, Jon Roesler, and Mark Kinde are epidemiologists with the Minnesota Department of Health’s Injury and Violence Prevention Unit.

Acknowledgments The authors wish to thank Anna Gaichas for her input on sample design, development of the dog bite abstraction form, and ideas for data analysis; Don Bishop, Ph.D., Mary Winnett, M.D., M.P.H., Joni Scheftel, D.V.M., M.P.H., and Ayo Adeniyi, M.B.B.S., M.P.H., for their critical review of the manuscript; Sara Westberg for her work with the abstraction form and for her leadership and support of the abstraction staff; and Joe Russel, Karen Thomas, M.P.H., Angela Marr, M.P.H., and Victor Coronado, M.D., of the CDC National Center for Injury Prevention and Control for their feedback and support.